AB1532 ULTRASOUND ASSESSMENT OF A1 AND A2 PULLEY ENTHESIS WITH ANATOMICAL AND HISTOLOGICAL CORRELATION
Authors: L. Coronel, M. Miguel, J. Blasi, S. Marsal, M. A. D’agostino, I. Möller
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Digital entheses are of particular interest in inflammatory arthritis. The annular pulleys (A) are forms of soft connective tissue organized as transverse fibers of variable width, thickness, and configuration that overlay the synovial sheath of flexor tendons. These structures prevent the flexor tendons from bowing and maintain them in constant relationship to the joint axis of motion. <h3>Objectives</h3> To describe and measure the ultrasonographic, anatomical, and histological characteristics of the A1 and A2 annular pulleys entheses. <h3>Methods</h3> A1 and A2 annular pulleys from 15 formalin-embalmed cadavers were assessed by grey-scale ultrasound (Figure 1) and then dissected. The ultrasonographic evaluations included the identification, widths, and characterization of insertion site of the annular pulleys. For the anatomical analysis, dissection was then performed, identifying the transverse fibers of the distal region of the palmar fascia as the proximal limit and the proximal interphalangeal joint as the distal limit. Measurements of the anatomical width of the pulleys were obtained with a digital caliper. For the histological study, 2x2 cm samples were received, fixed with 4% formaldehyde, and processed to obtain paraffin blocks, then cut into 4-micron sections and stained with hematoxylin-eosin. The slides were observed and measured with a Leica DMD 108 microscope. Quantitative data were expressed as mean ± standard deviation (SD) and qualitative data as n (%). Means were analyzed using Student's t-test and frequencies using the chi-square test and Fisher test when needed. Pearson's correlation coefficient (r) was used to analyze the linear correlation between the ultrasonographic and anatomical measurements. Statistical analyses will be performed using the SPSS program version 26.0. <h3>Results</h3> Fifteen cadaveric hands (9 males and six females) with a mean age of 79 years were included. Regarding the ultrasonographic assessment the mean ultrasound width of the A1 pulley was 0.27 ± 0.06 mm and A2 0.11 mm ± 0.04 mm in the thumb, while A1 was 0.36 ± 0.09 mm and A2 pulley 0.46 ± 0.06 mm on the other fingers. A strong correlation between the ultrasonographic and anatomical measurements was found (r=0.82). All A1 in the thumb shows sesamoid bones (SB) in the radial and ulnar sides where the annular pulley make its proximal attachment, while SB was found in just twelve hands in the second finger (80%) and two hands (13%) in the fifth finger. The histological description of the annular pulleys shows a well-vascularized outer surface and a fibrocartilaginous component in the inner surface. The insertion points at the sesamoid or the phalangeal bones demonstrate a diverse nature of the enthesis with fibrocartilaginous and fibrous areas. <h3>Conclusion</h3> These preliminary results show that ultrasound is a valuable tool for identifying annular pulleys' width and entheses, with good correlation with the anatomical and histological study. The annular pulleys have a mixed fibrous and fibrocartilaginous enthesis. <h3>References</h3> [1]Doyle JR. Anatomy of the finger flexor tendon sheath and pulley system. J Hand Surg. 1988 Jul;13(4):473–84. [2]Bianchi S, Martinoli C, de Gautard R, Gaignot C. Ultrasound of the digital flexor system: Normal and pathological findings. J Ultrasound. 2007 Jun;10(2):85–92. [3]Tanaka S, Uehara K, Sugimura R, Miura T, Ohe T, Tanaka S, et al. Evaluation of the first annular pulley stretch effect under isometric contraction of the flexor tendon in healthy volunteers and trigger finger patients using ultrasonography. BMC Musculoskelet Disord. 2021 Dec;22(1):421. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Luis Coronel Grant/research support from: Amgen, Maribel Miguel: None declared, Joan Blasi: None declared, Sara Marsal: None declared, Maria-Antonietta D'Agostino: None declared, Ingrid Möller: None declared.